Experimental Study On High Efficiency Plugging And Self-Plugging Removal Drilling Fluid Optimization In Fractured Reservoir

In order to solve the contradiction between the drilling plugging and completion plugging removal technology in fractured reservoir,in this paper,a set of self-adaptive plugging fluid system is developed,the main mechanism of cooperative pressure plugging and self plugging removal is revealed.The newly developed plugging fluid can not only effectively improve the adaptability and pressure-bearing effect of drilling plugging system,but also has the technical advantages of self plugging removal and reservoir protection through in-situ self hydrolysis chemical reaction.A new type of self degradation lost circulation materials was prepared by melt polycondensation with high purity LA as main raw material,Sn Cl₂ and A as catalysts.The newly prepared PLA self degradable plugging agent is a crystalline polymer,with good thermal stability.It can be processed by melt forming method,and has good dispersion and suspension stability in drilling fluid.The self degradation rate of the new self degradation plugging agent increases with temperature increasing.The acid and alkaline environment can promote its self degradation,and the inorganic salt does not affect its self degradation characteristics.Water molecules penetrate into the structure of the self degradation plugging agent,attack the amorphous structure,interact with the ester bond in the molecule,break the molecular chain of the polymer,and reduce the molecular weight.The molecular polymer products gradually fall off,and the in-situ hydrolysis reaction results in the self degradation plugging agent of PLA.A set of drilling and completion fluid system for reservoir protection was optimized by using the newly developed polylactic acid self degradation plugging agent with other lost circulation materials.The experimental evaluation shows that the drilling and completion fluid has good rheology,filtration,plugging,and in-situ self plugging removal characteristic to protect the reservoir.An elastic mesh plugging agent with temperature resistance of 150℃,tensile strength of175 k Pa and 50%compression permanent deformation rate of less than 10%was obtained.The synergistic plugging effect of elastic mesh plugging agent and bridging filling plugging material was discussed.Using the new self degradable plugging agent particles and self degradable plugging fiber,combined with different types of plugging materials such as elastic mesh plugging agent and common calcium carbonate particles,a set of self degradation plugging working fluid formula was obtained by experiments,which has good self-adaptive plugging effect,low fracture loss and in proper completion time It can solve the contradiction between high efficiency plugging and self plugging removal technology in the process of drilling and completion.